Electronic compasses are integrated in various electronic products to improve navigational performance or other functionalities of those products. For example, an electronic compass can be used in connection with a global positioning system (GPS) to improve position sensing. A traveling direction sensed by the GPS reflects movements of an object carrying the GPS. However, when the object stops or travels at a low speed, conventional GPS often cannot determine the orientation and position of the object. An electronic compass can provide information of a geomagnetic field, thereby improving the position sensing by the GPS.
Hall devices and magneto-resistive devices can usually provide sensing of an external magnetic field. Magneto-resistive devices, including anisotropic magneto-resistor (AMR), giant magneto-resistor (GMR), and tunneling magneto-resistor (TMR), may provide better sensitivity than Hall devices.
Existing magneto-resistive devices may have significant limitations depending on the devices or their configurations, designs, or applications. For example, AMR magnetic field sensors are generally limited to two-axis sensing. GMR magnetic field sensors can only operate in a unipolar mode, because they can detect only the magnitude of the sensed magnetic field but not the exact direction of the field. In addition, it may be difficult to achieve a multi-axis integrated magnetic field sensor using conventional GMR, TMR, or AMR.